Rhodium(I) and platinum(II) complexes with chelating bidentate isonitrile ligands

Abstract

Rhodium(I) complexes, [Rh(DiNC) 2]A, where A −  Cl −, BF 4 −, or BPh 4 −, and [Rh(t-BuDiNC) 2]A, where A −  Cl −, BPh 4 −, or PF 6 −, were prepared by reaction of [Rh(COD)Cl] 2 with the bidentate chelating isonitrile ligands, DiNC and t-BuDiNC. The solid compounds are variously colored yellow, green, blue or violet. In dilute (∼10 −5 M) solutions, the compounds are yellow, but as the concentrations of the solutions are increased, the colors become green or blue. Ultraviolet-visible spectroscopic studies suggest, as found previously for monodentate isonitrile rhodium(I) complexes, that the [Rh(DiNC) 2] + cation exists as a monomer in dilute solutions, but dimers, trimers, and tetramers are found at higher concentrations. For [Rh(t-BuDiNC) 2] +, only monomers and dimers are observed; presumably the bulky t-butyl groups prevent the formation of higher oligomers in this case. Equilibrium constants for the dimerizations of [Rh(DiNC) 2] + and [Rh(t-BuDiNC) 2] + were determined. When exposed to room light, blue solutions of the oligomers [Rh(DiNC) 2] x x+ fade to the yellow color of the monomer; 1H NMR spectra of the solutions confirm the photodissociation of the oligomers. The reaction of [Rh(DiNC) 2] + with I 2 yields the binuclear [Rh 2(DiNC) 4I 2] 2+ presumed to have a structure with a RhRh bond and terminal I − ligands. Under the same conditions, monodentate isonitrile complexes [Rh(CNAr) 4] + yield mononuclear [Rh(CNAr) 4I 2] + upon reaction with I 2. The greater stability of the dimeric structure for DiNC may be due to the smaller steric bulk of the DiNC ligand as a consequence of its near planarity as compared with monodentate CNAr ligands in which the Ar groups may rotate. Additional evidence for dimer stabilization by DiNC is the high temperature (70°C) required for RhRh bond cleavage as observed in 1H NMR studies of [Rh 2(DiNC) 4I 2] 2+. The yellow platinum(II) complex [Pt(DiNC) 2]PtCl 4 is isolated from the reaction of (Et 4N) 2PtCl 4 with DiNC. The reaction of K 2PtCl 4 with t-BuDiNC yields white cis-PtCl 2(t-BuDiNC). Complexes reported herein are characterized by their UV-visible, IR, and 1H and 13C NMR spectra.